1. Field of the Invention
The present invention relates to a heating apparatus suitable for use as a fixing apparatus of a copying machine, a printer, etc. using an electrostatic recording system or an electrophotographic recording system.
2. Related Art
In an image forming apparatus, such as a copying machine or a printer, a toner image is transferred to a transferring material by a photosensitive drum. Thereafter, heating/pressurizing processing is performed by a fixing heat roller to thereby effect image formation. The fixing heat roller is provided with a temperature sensor consisting of a thermistor or the like to perform temperature control. Generally speaking, a halogen heater is used as the means for heating the heat roller.
Recently, as a result of an increase in the operating speed of image forming apparatuses and the advent of color image forming apparatuses, the electric power supplied to the heating means for the heat roller has been increased in order to fix the toner on the transferring material in a stable manner through heating and pressurization.
In the above-mentioned conventional image forming apparatus, there is a further demand for an increase in speed, and to meet this demand, there is a necessity to substantially increase the electric power supply to the halogen heater used as the means for heating the heat roller.
Because of its characteristics, the halogen heater involves a large rush current flow at the time of power supply, and, as is pointed out, this can affect the commercial power source by causing a temporary reduction in voltage. In particular, in a halogen heater to which large power is supplied, the commercial power source is affected to a considerable degree.
Conventionally, to cope with a load with large rush current, phase control or the like to achieve a reduction in current supply angle in TRIAC, thyristor, SSR (solid state relay), etc. for controlling current supply to the halogen heater, is performed for a period of ten and several cycles of the commercial power frequency which is under the influence of the rush current.
However, when such phase control is executed, the TRIAC, thyristor, SSR or the like involves generation of a great radio noise at the time of switching.
It is an object of the present invention to provide a heating apparatus in which rush current is suppressed.
Another object of the present invention is to provide a heating apparatus which involves no noise generation even if AC current phase is controlled.
Still another object of the present invention is to provide a heating apparatus comprising:
a heat generating member;
a heating member heated by the heat generating member;
a temperature detecting member for detecting the temperature of the heating member; and
power supply control means for controlling power supply to the heat generating member on the basis of a detection output of the temperature detecting member,
the power supply control means including a first power supply control for applying an AC voltage of a limited phase to the heat generating member and a second power supply control for applying an AC voltage of an unlimited phase to the heat generating member,
wherein turning ON/OFF of power supply to the heat generating member on the basis of a detection output of the temperature detecting member is not effected during the first power supply control.
The other objects of the present invention become apparent from the following description.